When a transmitting device sends a data to a receiving device, there are cases that because some part of the data is lost (has disappeared), only the other part of the data arrives at the receiving device. Further, when the transmitting device sends a data to the receiving device, there are cases that because some part of the data is accumulated within the communication network, the arrival of the data at the receiving device is too late (the delay time, which is the time from the transmitting device sending the data to the data arriving at the receiving device, becomes too long).
Among the data sent by the transmitting device, the amount of the data (the data arrival amount) having arrived at (or being received by) the receiving device per unit time is called throughput.
For example, if the transmitting device sends a data to the receiving device at a transmission rate of 4 Mbps, then it is assumed that 25% of the data (that is, a part corresponding to 1 Mbps) is lost. Here, the transmission rate is the amount of the data sent by the transmitting device per unit time. In this case, the receiving device receives the data at 3 Mbps. That is, the throughput is 3 Mbps.
Further, even if no data is lost, it is still assumed that the receiving device receives the data at 3 Mbps because of the increase in delay time. In this case, the throughput is also 3 Mbps.
If the data sent from the transmitting device to the receiving device is multimedia data such as video and/or audio data, then any loss of the data may cause noise to occur in the video and/or audio. Further, an excessive delay time may possibly bring a stop to the play of the video and/or audio.
Therefore, it is considered as preferable to estimate the throughput with a high accuracy, and adjust the data size of the multimedia data sent by the transmitting device based on the estimated throughput. Hence, techniques for estimating the throughput are being developed. The throughput estimation devices disclosed in the following Patent Document 1 through Patent Document 6 are known as such kind of techniques.
Patent Document 1: Pamphlet of WO 08/143,026
Patent Document 2: JP 2004-254025 A
Patent Document 3: JP 2005-244851 A
Patent Document 4: JP 2007-116329 A
Patent Document 5: JP 2008-258877 A
Patent Document 6: JP 2008-278207 A
However, such a case can be assumed as to apply the above throughput estimation devices to a mobile communication system in which a mobile station (a receiving device) and a transmitting device are communicably connected via a wireless link established between the mobile station and a base station on a mobile communication network.
In this case, even for a constant transmission rate, the data transmission rate through the wireless link still changes with any change in the quality of the wireless link (the wireless link quality). As a result, the throughput also changes. Here, the data transmission rate is the amount of the data transmitted per unit time through the wireless link.
Referring to FIGS. 1A to 1C, the throughput change with the change in the wireless link quality will be explained in more detail.
The pipes in FIGS. 1A to 1C denote a wireless link. FIGS. 1A to 1C show that the thicker the pipe, the higher the data transmission rate through the wireless link (i.e. the higher the wireless link quality).
The arrows entering in the pipe denote the transmission rate. FIGS. 1A to 1C show that the more the number of the arrows entering in the pipe, the higher the transmission rate. Further, the arrows exiting from the pipe denote the throughput. FIGS. 1A to 1C show that the more the number of the arrows exiting from the pipe, the higher the throughput.
FIG. 1A shows that both the wireless link quality and the throughput are at the highest level. FIG. 1B shows that both the wireless link quality and the throughput are at the lowest level. FIG. 1C shows that both the wireless link quality and the throughput are at the second highest level. In this manner, the throughput also changes with the change in the wireless link quality.
However, the above throughput estimation devices estimate the throughput without being based on the wireless link quality. Therefore, it is liable to be unable to estimate the throughput with a high accuracy when the data is sent via the wireless link.